util: add getbefloat64...
util: add getbefloat64
As far as I can tell, this is wrong. double's format isn't strictly
specified in the C standard, but the wikipedia article implies that
platforms implementing optional Annex F "IEC 60559 floating-point
arithmetic" will work correctly.
My local C experts believe doing *((double *) &t) is a strict aliasing
violation, and that using a union is also one. Doing memcpy appears to
be the least-undefined behavior possible.